In a power distribution network, one or more distributed phases can become faulted to ground. Reasons for such a ground fault are numerous and known, and include damage to electrical insulation and the connection of a defective device to the power network, among others.
In high-impedance grounded networks and ungrounded networks (i.e., any network where there is no significant current path to ground), phase-to-ground faults produce relatively insignificant values of fault current. Typically, in small isolated-neutral industrial installations, the ground-fault current for a phase fault may be well under an amp. Correspondingly, in a large plant containing miles of cable, such current may be no more than 20 amps. Such currents usually are not of sufficient magnitude for the operation of zero-sequence over-current relays, ground fault relays, fault-sensing circuit breakers, fuses, and similar protective devices to locate and remove such faults. Such protective devices do not have the sensitivity necessary due to the complexity of the current flow pattern between the distributed cable capacitance and the fault.
The primary indication of a ground fault in such a network is a shift in ground potential with respect to phase voltage. Although such indication can be sensed and employed as an alerting device, such indication does not assist in determining the location of the ground fault, which may be anywhere within the network.
An accurate ground fault location system is an important tool that is useful in minimizing the economic and maintenance impact of faults on ungrounded and high impedance grounded networks. The benefits of accurate fault location include reduced switching operations required to isolate a faulted feeder section or load; reduced search efforts to locate a fault, thereby facilitating faster repair time; and greater likelihood that a detected fault will be addressed before a second fault occurs in the network. Accordingly, a need exists for an accurate ground fault location system and a detector therefor.